Built-in checking of the correct self-test signature

A procedure is described for determining the initial value of a single or multiple input signature register (used to compress responses in built-in testing) so that the final good-machine signature is always constant, e.g. all zeros. In this way, it is possible to determine if a fault has been detected by ORing the outputs of the register stages. Since the OR operation can be built-in, a single observation of the output of the OR gate will determine if the circuit has passed the test